Pandemic influenza refers to a global outbreak of a new strain of the influenza virus that spreads easily from person to person. Unlike seasonal flu, which occurs regularly, a pandemic can affect a large portion of the population and lead to significant illness and death. This occurs when a virus mutates and people have little or no immunity against it. Historically, pandemics have caused widespread health crises, such as the 1918 Spanish flu, which resulted in millions of deaths worldwide. Public health measures, including vaccination and social distancing, are crucial in managing the spread of pandemic influenza and protecting vulnerable populations.